I get something similar every once in a while when loading a new screen (combat or merchant/count/tavern), but alt-tabbing FIXES it. The textures get scrambled - they are recognisable - say the brick wall texture will appear instead of the grass texture, or the tree texture will appear instead of the brick wall texture, or wierdest - the armour textures will appear instead of the grass texture...
An ASUS Geforce 3 video card...